In my opinion, the best way is to choose the right cryptocurrency exchange and trade. We don't know how valuable bitcoin will be by the end of this year, I'm not so optimistic about that.

yes, that's right. I think that's the key to success
the exchange which you've inset - CoinDeal is one of my favourite exchanges this times, the most important advantage to me is the fact that I can vote on the next available currencies

After reading this article, I've started to disagree that Libra will be cryptocurrency at all. We still don't know much about this coin, but all signs suggests that this will be an exact opposite of cryptocurrency ideals

It's hard to say which one is "better". They have a very different agendas.
What concerns me, is the fact that Ethereum doesn't seems to follow the growing trend of BTC (Blockchain24 recently post a nice analysis about it).

Significant part of crypto enthusiasts is gathered on reddit, so I believe this is a place worth of mentioning.
As for most interesting subreddits, here you have my personal favorite list:
r/CryptoCurrency - the most general one of all crypto subreddits, which is not focused on one coin (like most of them do) but on whole crypto world
r/CryptoCurrencies - smaller sub than previous one, but I believe it's interesting too
r/altcoin - as the name suggests, this sub is focused on coin other than btc
r/Crypto_Currency_News - this one is mainly for posting news
r/BlockChain24 - similar to previous one, but focused on blockchain tech itself

It is not too late I think, it must be your decision based on experience/opinions. Also, it is easy to enter crypto world because of new ways to invest in BTC e.g BuyCoinNow which let buy bitcoin without registration and sharing data so the whole process is a bit faster and safer

It's good way to acquire BTC, but still, if you want to trade and actually gain something on this, then you have to register on exchange eventually.

I believe it's at least worth of consideration. The current grow of price is slow, but it should be stable. It's good to buy some coins now and see how the situation will develop (not exactly already on exchange, but maybe on sites like Buy Coin Now, when you'll get coins directly to your wallet). But of course, do it only in case when you have some spare money which you're ready to invest

It could be tricky to do so. Cryptocurrencies are good as additional source of money, but if you relay on them in 100% then you are at the mercy of the market